Blood-gas sampler

ABSTRACT

A syringe comprising a hollow barrel and a coaxial plunger, the plunger having an improved seal at the leading end thereof wherein a minimal resistance to arterial blood aspiration results but increased resistance through pressure-buckling at a thin-wall groove is provided as a result of opposed pressure forces during discharge of blood from the hollow of the barrel. Thus, a material increase in seal resistance against blood leakage across the seal is obtained.

United States Patent 1 Moorehead June 24, 1975 1 BLOOD-GAS SAMPLER [75]Inventor: Harvey Robert Moorehead, Salt Lake City, Utah [73] Assignee:Deseret Pharmaceutical Co., Inc.,

Sandy, Utah [22] Filed: June 27, 1974 [21] Appl. No.1 483,594

[52] U.S. Cl 128/2 F; 128/218 P; 128/DIG. 5 [51] Int. Cl. A61B 5/14;A6lM 5/315 [58] Field of Search.... 128/218 P, 219, 2 F, 218 M,

128/276, 220, 234, 218 R, DIG. 5, 218 D, 278

[56] References Cited UNITED STATES PATENTS 1,348,796 8/1920 Gronbech128/219 3,147,753 9/1964 Nogier et a1 128/218 P 3,255,752 6/1966 Dick3,291,128 12/1966 ONeil... 3,306,291 2/1967 Burke 128/218 R 3,659,7495/1972 Schwartz 128/218 M 3,678,930 7/1972 Schwartz 128/218 P FOREIGNPATENTS OR APPLICATIONS 233,551 4/1960 Australia 128/218 P 1,106,8253/1968 United Kingdom 128/218 R Primary Examiner-RichardA. GaudetAssistant Examiner-J. C. McGowan Attorney, Agent, or Firm-Lynn G. Foster[57] ABSTRACT A syringe comprising a hollow barrel and a coaxialplunger, the plunger having an improved seal at the leading end thereofwherein a minimal resistance to arterial blood aspiration results butincreased resistance through pressure-buckling at a thin-wall groove isprovided as a result of opposed pressure forces during discharge ofblood from the hollow of the barrel. Thus, a material increase in sealresistance against blood leakage across the seal is obtained.

7 Claims, 4 Drawing Figures BLOOD-GAS SAMPLER BACKGROUND 1. Field ofInvention The present invention relates generally to blood-gas analysisand more particularly to a blood-gas sampler comprising a syringe havinga novel seal at the leading end of the plunger.

2. Prior Art Prior art blood-gas sampling syringes have utilizedrelatively unsatisfactory seals between the plunger and barrel of thesyringe. Most frequently the syringe barrels are of glass, butoccasionally of plastic. The mentioned seals are of a relatively hardelastomer and consist primarily of two or three annularly enlargedrings, each creating a relatively wide high friction sealing contactwith the interior surface of the barrel. The same high level ofseal-created friction exists both when advancing and when retracting theplunger within the barrel. With such seals it has been impossible forsuch syringes to self aspirate in receiving a sample of blood followingarterial penetration. Manual aspiration has been obligatory. Whereconstant seal friction is reduced overall aspiration solely under theforce of arterial pressure can be achieved but such would be followed byappreciable leakage around the seal as the blood sample is subsequentlyexpelled from the barrel of thesyringe under manual pressure applied toadvance the plunger.

BRIEF SUMMARY AND OBJECTS OF THE PRESENT INVENTION In its presentlypreferred form the present invention comprises a blood-gas arterialsyringe comprising a ho]- low barrel and a plunger situated within thebarrel. An improved seal spans between the leading end of the plungerand the interior surface of the barrel. The seal comprises a cup-shapedbody which defines an annular wall extending essentially coaxial to butspaced from the inside surface of the intermediate portion of the barreland also comprises an end closure at the leading end of the seal. Thebody of the seal is affixed at its trailing end to the leading end of anintermediate section of the plunger. A radially extending annular ringor bead of the seal sealingly engages the interior surface of the barrelcreating only limited resistance to plunger extension under force ofarterial pressure. An

- annular groove along the inside of the annular wall of the sealcreates a reduced thickness annular buckling region which is forcedradially outward into sealing engagement as the plunger is displacedinto the barrel by the user causing blood within the barrel to beexpelled under substantial pressure through a relatively small diameterport disposed at the forward end of the barrel whereby blood leakageacross the seal is greatly alleviated, if not non-existent.

With the foregoing in mind, it is a primary object of the presentinvention to provide an improved blood-gas arterial sampling syringe.

It is a further paramount object of the present invention to provide, ina blood-gas arterial sampling syringe, an improved seal interposedbetween the leading end of a plunger and the hollow interior surface ofa barrel which creates only limited seal resistance to plunger extensionunder force of arterial pressure but substantially greater resistance asthe plunger is displaced into the barrel and blood is expressed from thesmall orifice at the leading end of the barrel whereby blood leakageacross the seal is greatly alleviated.

These and other objects and features of the present invention will beapparent from the following detailed description, taken with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective representation ofa presently preferred blood-gas arterial sampling syringe according tothe present invention;

FIG. 2 is an enlarged longitudinal cross section of the mentionedsyringe taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary cross section showing the seal, whichis interposed between the barrel and the plunger in the position assumedduring blood aspiration; and

FIG. 4 is a fragmentary cross section similar to FIG. 3 but showing theseal in the position assumed during discharge of blood from a barrel ofthe syringe.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT With reference to theFigures, a presently preferred embodiment of the present invention isillustrated comprising a blood-gas sampling syringe 10 having a barrell2 and a plunger 14. The barrel is preferably lighttransmitting and ismade of glass or plastic material, such that gas permeation isnegligible. The barrel 12 comprises a forwardly directed converging wallsection 16 defining a relatively small diameter port or orifice 18. Theprojection 16 is adapted to receive an arterial needle in a conventionalmanner whereby blood from an artery of the patient enters the barrel 12through the port passage 18.

The barrel 12 also comprises an intermediate portion 20 comprising anannular wall of uniform inside and outside diameter whereby acylindrical hollow interior 22 consisting of a blood-receiving chamberis defined. The hollow chamber 22 terminates at the trailing end of thebarrel 12 at opening 24, the diameter of which is essentially equal tothe inside diameter of the chamber 22. A flange 26 projects radiallyoutwardly away from the opening 24 at the trailing end of the barrel 12.The flange 26 provides for finger engagement by the user accommodatingadvancement of the plunger 14 into the barrel 12 to express blood fromthe chamber 22 in a manner hereinafter more fully described.

The plunger 14 may be of one-piece molded construction. As illustrated,it comprises a radially enlarged cap or handle 30 bonded at lap joint 32to an elongated intermediate section comprising a hollow tube 34. Abonded lap joint 36 secures a reduced diameter trailing end portion 38of an elastomeric head or seal 40 to the leading end of the intermediatetubular section 34.

The elastomeric head or seal 40 is preferably comprised of some highlypliable synthetic resinous material, such as soft vinyl, to facilitateease of aspiration as hereinafter more fully described. The seal 40comprises an annular thin wall body 42, said wall having a reducedthickness at an annular groove 44 disposed centrally between the leadingend of the tubular intermediate section 34 and a thin wall end closure46 of the seal 40. An annular bead or ring 48 extends into sealingcontact with the interior surface of the intermediate portion 20 of thebarrel 12 in such a fashion as to create very little resistance toplunger extension, the bead 48 being situated at or near the interfacebetween the closure end 46 and the annular wall 42 of the seal 40. Thus,the radially extending annular bead for ring 48 creates only a modestseal against the interior surface of the barrel while producing littleresistance to the extension of the plunger responsive solely to theforce of arterial pressure once needle penetration of an artery has beenaccomplished. Hence, the sampling syringe 10 is self-aspirating.

The annular wall 42 of the seal 40 is coaxial with the longitudinal axisof the syringe l and barrel 12, being spaced therefrom during aspirationas illustrated in FIGS. 2 and 3. However, experimentation has shown thatthe seal created by the relatively small annular bead 48 is inadequateto prevent blood leakage across the bead 48 as the user of the syringemanually advances the plunger 14 into the barrel 12 to expel blood fromthe hollow chamber 22 through the small diameter port 18 undersubstantial pressure. To alleviate or prevent the mentioned bloodleakage problem, the annular wall 42 is provided with the mentionedannular groove 44, centrally and radially disposed along the interiorsurface of the wall portion 42. Because of the indicated configuration,as force is applied to the cap of the plunger 14 as shown at arrow 54 toexpel blood from the chamber 22, the relatively yieldable seal bucklesradially outwardly along the annular region of the wall 42 at groove 44,under fluid pressure illustrated by arrows 52, into sealing engagementwith the interior surface of the barrel 12. See FIG. 4. Thus, an annularbead results which is of substantial thickness and in nearly allsituations totally prohibits blood loss across the seal 40.

Thus, the seal 40 accommodates easy self-aspiration of the samplingsyringe 10 so that arterial pressure alone will fill the chamber 22 andat the same time creates a major additional sealing bed during thoseoccasions when the plunger is advanced to expel part or all of a bloodspecimen from the chamber 22. In this way blood leakage across the sealis alleviated or prohibited.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. A blood-gas arterial syringe comprising:

a hollow barrel having means at the leading end for receiving anarterial needle, said means comprising a relatively small diameter portwhereby blood is communicated from an artery to the hollow of thebarrel, the barrel further comprising an intermediate portion having arelatively large essentially uniform inside diameter which opens at thetrailing end of the barrel;

a plunger normally extending through the said opening and disposed alongthe intermediate portion of the barrel, the plunger comprising means atthe trailing end for advancing the plunger into the barre], and anintermediate section having a lateral dimension less than said insidediameter of the intermediate portion of the barrel;

the improvement comprising a seal comprising a cupshaped body initiallydefining an essentially annular wall coaxial to but spaced from theinside surface of the intermediate portion of the barrel and an endclosure comprising the leading end of the seal, the body being united atits trailing end to the leading end of the intermediate section of theplunger, the seal further comprising at least one radially extendingannular seal bead spanning at all times between the annular wall and theinside surface of the intermediate portion of the barrel creating onlylimited resistance to plunger extension under force of arterialpressure, the seal further comprising a reduced thickness section of theannular wall located forward of said union between said trailing end ofthe seal and the leading end of the intermediate section of the plungerand creating an annular buckling region which is forced radially outwardby fluid pressure creating an additional temporary annulus in sealingcontact with the inside surface of the barrel as the plunger is advancedinto the barrel causing blood within the barrel to be expelled throughthe small diameter port whereby blood leakage across the seal isalleviated, the temporary annulus collapsing to the initialconfiguration when the plunger is no longer advanced.

2. The syringe of claim 1 wherein said annular seal bead is disposedadjacent the interface between the end closure and the annular wall ofthe seal.

3. The syringe of claim 2 wherein said annular buckling region isdisposed essentially midway between the leading end of the intermediatesection of the plunger and the annular seal bead.

4. The syringe of claim 1 wherein said barrel is composed oflight-transmitting material.

5. The syringe of claim 1 wherein the seal is affixed at its trailingend to the intermediate section of the plunger at a lap joint.

6. The syringe of claim 1 wherein said seal comprises a soft elastomericmaterial.

7. The syringe of claim 1 wherein said reduced thickness sectioncomprises an annular groove along the inside of the annular wall of theseal, which is free from contact with the intermediate section of theplunger.

1. A blood-gas arterial syringe comprising: a hollow barrel having meansat the leading end for receiving an arterial needle, said meanscomprising a relatively small diameter port whereby blood iscommunicated from an artery to the hollow of the barrel, the barrelfurther comprising an intermediate portion having a relatively largeessentially uniform inside diameter which opens at the trailing end ofthe barrel; a plunger normally extending through the said opening anddisposed along the intermediate portion of the barrel, the plungercomprising means at the trailing end for advancing the plunger into thebarrel, and an intermediate section having a lateral dimension less thansaid inside diameter of the intermediate portion of the barrel; theimprovement comprising a seal comprising a cup-shaped body initiallydefining an essentially annular wall coaxial to but spaced from theinside surface of the intermediate portion of the barrel and an endclosure comprising the leading end of the seal, the body being united atits trailing end to the leading end of the intermediate section of theplunger, the seal further comprising at least one radially extendingannular seal bead spanning at all times between the annular wall and theinside surface of the intermediate portion of the barrel creating onlylimited resistance to plunger extension under force of arterialpressure, the seal further comprising a reduced thickness section of theannular wall located forward of said union between said trailing end ofthe seal and the leading end of the intermediate section of the plungerand creating an annular buckling region which is forced radially outwardby fluid pressure creating an additional temporary annulus in sealingcontact with the inside surface of the barrel as the plunger is advancedinto the barrel causing blood within the barrel to be expelled throughthe small diameter port whereby blood leakage across the seal isalleviated, the temporary annulus collapsing to the initialconfiguration when the plunger is no longer advanced.
 2. The syringe ofclaim 1 wherein said annular seal bead is disposed adjacent theinterface between the end closure and the annular wall of the seal. 3.The syringe of claim 2 wherein said annular buckling region is disposedessentially midway between the leading end of the intermediate sectionof the plunger and the annular seal bead.
 4. The syringe of claim 1wherein said barrel is composed of light-transmitting material.
 5. Thesyringe of claim 1 wherein the seal is affixed at its trailing end tothe intermediate section of the plunger at a lap joint.
 6. The syringeof claim 1 wherein said seal comprises a soft elastomeric material. 7.The syringe of claim 1 wherein said reduced thickness section comprisesan annular groove along the inside of the annular wall of the seal,which is free from contact with the intermediate section of the plunger.